Production of water-soluble aromatic resin sulfonates by sulfonating with so3 in liquid so2



PRODUCTIQN OF WATER-SOLUBLE AROMATIC RESEI SULFONATES BY SULFONATINGWITH S lN LIQUID S0 William C. Bauman, Midland, and Harold H. Roth, BayCity, Mich assignors to The Dow Chemical Company,

Midland, Mich, a corporation of Delaware No Drawing. Application August19, 1953 Serial No. 375,283

8 Claims. (Cl. 260-785) This invention concerns an improved method forthe production of water-soluble sulfonates of resinous aromaticmaterials. It pertains more particularly to the sulfonation of certainsolid thermoplastic copolymers of alkenyl aromatic compounds such asstyrene, vinyltolnone, or vinylxylene, etc., in the presence of liquidsulfur dioxide as a reaction medium.

It is known that the resin sulfonates obtained by sulfonatingpolystyrene, or any of a variety of other solid thermoplastic polymersof alkenyl aromatic compounds vary widely in properties, e. g. frombeing solid waterinsoluble materials to being gummy masses which arealso insoluble, or only partially soluble, in water, to being non-gummymaterials which are partially or cornpletcly soluble in water, dependingon the'conditions under which the sulfonation is carried out.Water-soluble sulfonates of polystyrene have heretofore been prepared bydissolving polystyrene in a liquid polychlorinatcd aliphatic hydrocarbonsuch as carbon tetrachloride, or chloroform, etc., and treating thesolution with a highly reactive sulfonating agent such as chlorosulfonicacid. Even when operating in such manner, the properties of the product,e. g. the ease or completeness with which it can be dissolved ordispersed in water and its efiectiveness in increasing the viscosity ofwater to which it is added, vary considerably with slight changes in oneor more of the reaction conditions such as the kind or proportion of thesulfonating agent, the order or rate of mixing the starting materials,and the reaction temperature, etc. For these reasons it is diflicult,even when operating on a laboratory scale, to sulfonate successivebatches of a polymer and obtain the same quality of sulfonated product.The difficulty of reproducing the results becomes greater as thequantity of material handled is increased, e. g. from laboratory amountsto' a commercial scale. Many of the erratic results which have beenobtained are attributed to occurrence of side reactions such as areaction between a portion of the sulfonating agent and thepolychlorinated aliphatic hydrocarbon used as the reaction medium,cleavage of the polymer molecules, and formation of sulfone-typecrosslinkages between the polymer molecules. In addition to thedifiiculties just mentioned, the sulfonated polymers usually containionizable impurities such as unconsumed sulfonating agent, sulfuricacid, or hydrochloric acid, and, in some instances, inorganic salts suchas sodium sulfate or sodium chloride, etc., and extra steps are requiredfor removal of the impurities. V

In a copending application, SerialNo. 272,888, filed February 21, 1952,now Patent No. 2,691,644, of H. H. Roth, it is disclosed that many ofthe above difficulties involved in producing water-soluble sulfonatedresins can be avoided by sulfonating polystyrene, or similar resins,with sulfur trioxide in the presence of a liquid mixed solventconsisting of sulfur dioxide and a poly- States Patent chloride,o'r"tetrac'h1oroethylene, etc. However, the

polymers then tested could not satisfactorily be sulfonated to obtainwater-soluble products when using either of the indivdual ingredients ofsaid mixed solvent as the reaction medium. This fact is indicated in theapplication.

It has now been found that there are a number of solid thermoplasticpolymers composed principally of alkenyl aromatic compounds, e. g.styrene, or a'r-vinyltoluene, etc, which can satisfactorily besulfonated in the presence of liquid sulfur dioxide as a medium toobtain water-soluble sulfonated resin products. By water-soluble" it ismeant that the sulfonated resins can be dissolved, or dispersed bystirring, directly in water to form a substantially homogeneous liquidbody, e. g. a true or a colloidal solution thereof.

it has further been found that use of liquid sulfur dioxide as thesulfonation medium is advantageous in that the sulfur dioxide is inertto the sulfur trioxide and in that the sulfonated resin productprecipitates therefrom leaving most, if not all, of the impurities, e.g. unconsumed sulfur trioxide, dissolved in the liquid sulfur dioxidewhich may be drained or Washed from the product to obtain the latterdirectly in a form of good purity. Any liquid sulfur dioxide retained onsurfaces of the product is readily removed by vaporization.

it has still further been found that the alkenyl aromatic resins thatcan be sulfonated by the present method to form water-soluble resinsulfonates vary considerably as regards the extent to which they undergoone or both of the aforementioned side-reactions during the sulfonation.The copolymers of nuclear alkylated styrene compounds such asar-vinyltoluene, ar-vinylxyle'ne, or a'r-ethylstyrene, which aresuitable for use in the present process are more resistant to occurrenceof side reactions, especially formation of cross-linkages between thepolymer molecules, than are the corresponding copolymers of styrene, andare preferred.

The solid, thermoplastic alkenyl aromatic resins that can be reactedwith sulfur trioxide in the presence of liquid sulfur dioxide as thereaction medium to form Water-soluble resin sulfonates are onescontaining a total of at least 60 percent by Weight of at least onechemically combined monoalkenyl aromatic compound having the generalformula:

wherein R, R and R" independently represent members of the groupconsisting of hydrogen and lower alkyl radicals, especially the methylradical, and which have present in the resin molecule a functional groupthat renders the resin soluble, or readily dispersible, in liquid sulfurdioxide. Stated another way, any alkenyl aromatic resin that can, bymoderate stirring, be dissolved, or dispersed, in liquid sulfur dioxideto form a clear or cloudy liquid body free from a distinct separatelayer or precipitate of resinous material can satisfactorily besuifonated by the method of the invention, and such resins containing 60percent by weight or more of an alkenyi aromatic compound can besulfonated to obtain watersoluble resin sulfonates. A simple test todetermine whether a given alkenyl aromatic resin of the above statedcomposition is suitable for use in the process of the invention is toform a mixture of 5 parts by weight of the finely divided resin andparts of liquid sulfur dioxide, shake the mixture in a closedpressure-resistant vessel at 30 C. for 2 hours, and then allow themixture to stand without agitation at 30 C. for another 5 minutes. Ifthe mixture is then substantially homogeneous, i. e. if it is a clear orcloudy liquid free of a distinct separate layer, or precipitate, theresin can satisfactorily be used in the sulfonation process of theinvention, but if the mixture consists of two or more distinct layers,the resin is not suitable for use in the method. The homopolymers ofvinyl aromatic hydrocarbons such as styrene or vinyltoluene fail to meetthis test, i. e. the mixtures formed comprise a layer of liquid sulfurdioxide and a distinct layer of the resin which usually is in a swollen,gummy condition. When attempt is made to sulfonate polystyrene or thehomopolymer of vinyltoluene by the procedure of the invention, thesulfonated product usually comprises a considerable amount of resinousmaterial that is insoluble and not dispersible by stirring, in water.

Examples of solid, thermoplastic alkenyl aromatic resins which can besulfonated with sulfur trioxide in liquid sulfur dioxide as the mediumto obtain Watersoluble resin sulfonates are the copolymers of from 70 to98 weight percent of styrene and from 30 to 2 percent acrylonitriie;copolymers of from 65 to 98 percent arvinyltoluene and from 35 to 2percent acrylonitrile; copolymers of styrene, vinyltoluene and from 2 to35 percent acrylonitrile, copolymers of from 60 to 75 percentalpha-methylstyrene, 20 to 25 percent acrylonitrile, and 5 to percentethyl'methacrylate; copolymers of styrene and sulfur dioxide; copolymersof from 68 to 95 percent of either or both of the compounds styrene andar-vinyltoluene and from 5 to 32 percent of maleic anhydride; copolymersof from 60 to 87 percent of either or both of the compounds styrene andar-vinyltoluene and from 13 to 40 percent of methyl methacrylate; thecopolymer of 75 percent styrene and 25 percent ethyl acrylate; andcopolymers of styrene or arr-vinyltoluene with from 2 to 10 percent ofmethyl isopropenyl ketone; etc. All of the copolymers just mentioned arealkenyl aromatic resins which contain in the polymer molecule anon-olefinic aliphatic radical, such as a carbonyl, a carbonyloxy, or anitrile radical, having a carbon atom attached by more than one valenceto another atom, e. g. of oxygen or nitrogen, etc. The presence of suchradical, or radicals, is apparently necessary for satisfactoryemployment of the resins in the process of the invention. However, thepresence of too small or too large a proportion of such radicals in thecopolymer molecules sometimes prevents satisfactory employment of thecopolymers in the process of the invention. For instance, copolymers ofstyrene and acrylonitrile which contain less than 2, or more than 30percent by weight of chemically combined acrylonitrile are not readilydispersible in liquid sulfur dioxide and cannot satisfactorily besulfonated to form water-soluble resin sulfonates by the method of theinvention. As hereinbefore mentioned, the alkenyl aromatic resins whichare suitable can be dispersed by mild stirring in 19 times their weightof liquid sulfur dioxide at 30 C. Whether a given alkenyl 'aromaticresin can satisfactorily be sulfonated by the present process may bepredetermined by this simple test.

Although all alkenyl aromatic resins having the aforestated compositionsand meeting the above test, can be sulfonated by the present method toobtain watersoluble resin sulfonates, the extent to which side reactionsoccur during the sulfonation and the ease of repeating a givensulfonation to obtain the same quality of product are dependent on thekind of alkenyl aromatic resin employed. The copolymers containingstyrene as the only alkenyl aromatic compound chemically combinedtherein, tend to become cross-linked to an appreciable extent during thesulfonation reaction. The formation of a few cross-linkages between thepolymer molecules tends to increase both the average molecular weight ofthe sulfonated resin product and its effectiveness in thickening, i. e.increasing the viscosity of, Water in which it is dissolved, butextensive cross-linkage formation often renders the product insolubleand non-dispersible in water. With certain of such styrene copolymers,e. g. copolymers of styrene and sulfur dioxide, the tendencies justmentioned are offset by occurrence of scission of the polymer moleculesduring the sulfonation. In contrast, the corresponding copolymers ofnuclear alkylated styrenes such as vinyltoluene, vinylxylene, andethylvinylbenzcne, undergo the formation of cross-linkages between thepolymer molecules to a far less, and usually an inconsequential, extentduring sulfonation by the method of the invention. However, certain ofthe copolymers of nuclear alkylated styrenes, e. g. the copolymers ofvinyltoluene and sulfur dioxide, tend to undergo polymer chain scissionto a considerable extent during the sulfonation. The liquid sulfurdioxide-dispersible copolymers of nuclear alkylated styrenes withacrylonitrile, or with an unsaturated carboxylic acid, or an anhydrideor ester of such acid, are exceptionally resistant to occurrence of theaforementioned side reactions while being sulfonated by the presentmethod and are preferably employed. Such copolymers are alkenyl aromaticresins containing nitrile, carbonyl, or carbonyloxy radicals as the onlynon-hydrocarbon portions of the copolymer molecule. Examples of thesepreferred alkenyl aromatic resins are the sulfur dioxide dispersiblecopolymers of vinyltoluene and acrylonitrile, of vinyltoluene and methylmethacrylate, of vinyltoluene and methyl acrylate, of vinyltoluene andethyl acrylate, of vinylxylene and acrylonitrile, and of vinylxylene andmethyl methacrylate, etc.

The sulfonation is accomplished at temperatures not higher than 40 C.,e. g. between 40 and 40 C. and usually between -10 and 30 C., byadmixing at least 0.7, usually between 0.8 and 2, molecular equivalentsof sulfur trioxide with a dispersion in liquid sulfur dioxide of anamount of the alkenyl aromatic resin having a total of one molecularequivalent of one or more alkenyl aromatic compounds chemically combinedin the resin. The liquid sulfur dioxide may be employed in anyproportion large enough to form a substantially homogeneous dispersionof the resin starting material. The dispersion of resin in liquid sulfurdioxide usually contains 10 weight percent or less, e. g. from 1 to 5percent, of the resin, but the latter may be present in any proportioncapable of being dispersed in the sulfur dioxide. The sulfur trioxide ispreferably diluted, e. g. with an equal weight or more of sulfurdioxide, before being admixed with the resin dispersion.

The sulfur trioxide and the resin dispersion may be admixed in anyorder, e. g. by pouring the resin dispersion into a liquid solution ofsulfur trioxide in sulfur dioxide with stirring, or vice versa. Thereaction can be carried out in continuous manner by feeding separatestreams of the liquid sulfur dioxide-resin dispersion and of sulfurtrioxide, or. preferably a sulfur dioxide-sulfur trioxide solution, to amixing and reaction zone and withdrawing the reacted mixture, e. g. as astream, from the zone. The. reaction is carried out at a pressuresufficient to maintain a dispersion of the unreacted resin in liquidsulfur dioxide. It may be carried out at atmospheric pressure whenemploying reaction temperatures at or below -10 C., but at highertemperatures it is carried out at superatmospheric pressure, e. g. in abomb or autoclave. The tendency toward occurrence of the aforementionedside reactions, or the rate and extent of such side reactions, becomesgreater as the reaction temperature is raised. The sulfonation reactionis exothermic. However, the reaction mixture may be maintained at thedesired reaction temperature either by vaporization of a portion of theliquid sulfur dioxide or by external cooling of the reaction mixture.

The sulfonation occurs rapidly with formation of an alkenyl aromaticresin sulfonic acid which precipitates as small granules or particles.The product can be separated from the liquid sulfur dioxide in usualways, e. g. by filtering, decanting, or centrifuging the mixture. Any

unreacted sulfur trioxide or other impurities such. as sulfuric acidremain, for the most part, dissolved in the liquid sulfur dioxide. Thesolid resin sulfonic acid product may be washed with a small portion ofliquid sulfur dioxide to remove adhering mother liquor and any sulfurdioxide retained on the product may be removed by vaporization. Thewater-soluble alkenyl aromatic resin sulfonic acid may thus be obtaineddirectly in a solid granular form of good purity. Since thewater-soluble alkenyl aromatic resin sulfonic acids are usuallydeliquescent, the foregoing steps for separating the same arepreferably, but not necessarily, carried out in the absence of moistair, e. g. in a closed system.

The water-soluble alkenyl aromatic resin sulfonic acids may beneutralized in usual ways with alkalies such as ammonia, or sodium orpotassium hydroxide, etc., to form salts thereof. The ammonium andalkali metal salts thus obtained are soluble in water to form true orcolloidal solutions thereof. They are adapted for use as sizing agents.

The following examples describe ways in which the invention has beenpracticed, but are not to be construed as limiting its scope.

.EXAMPLE 1 In each of a series of experiments, 10 grams of a finelydivided copolymer, identified in Table I, was stirred together with 250ml. of liquid sulfur dioxide at 10 C. with formation of a clear toslightly cloudy solution, presumably of colloidal nature. A separatesolution of 5 ml. of liquid sulfur trioxide and 250 ml. of liquid sulfurdioxide was also formed at a temperature of l C. The two solutions werefed simultaneously and at about equal rates by volume, in from tominutes, to a reaction vessel which initially contained 500 ml. ofliquid sulfur dioxide. During feed of the materials, the mixture in thevessel was stirred and maintained at about -10 C. Upon mixing thestarting solutions, sulfonation occurred rapidly and a resin sulf-onicacid precipitated as a fine powder. The product was separated byfiltering, washed with diethyl ether, and dried under vacuum. A portionof the product was dissolved in water and neutralized with aqueoussodium hydroxide to form an aqueous solution containing 0.5 percent byweight of the sodium resin sulfonate. The aqueoussolutions thus formedwere more viscous than water. The following table identifies each solidcopolymer starting material by giving the kinds and percent by weight ofthe monomers chemically combined therein. It also gives the viscosity incentipoises at C. of each of the aqueous sodium resin sulfonatesolutions that was formed. In the table styrene is abbreviated as S,alpha-methylstyrene as AMS, acrylonitrile as VCN, and ar-vinyltoluene asVT.

Another series of experiments were carried out using a procedure similarto that described in Example 1, except that the alkenyl aromatic resinstarting materials were copolymers of styrene and maleic anhydridecontaining varying proportions of the latter. All of these copolymers,prior to being sulfonated, could be dispersed in liquid sulfur dioxideand those containing from 16 to 32 percent of maleic anhydride werereadily soluble and formed clear solutions. It may be mentioned thatpolystyrene and a copolymer of equal parts by .weight ,of styreneandmaleic acid have each been found not to. be not completely dispersiblein liquid sulfur dioxide'when tested as hereinbefore described. Asindicated above, all of the dispersible copolymers were sulfonated withsulfur trioxide using liquid sulfur dioxide as the medium and each ofthe granular resin sulfonic acid products was separated, dissolved inwater, and neutralized with sodium hydroxide to form a clear aqueoussolution containing 0.5 percent by weight of the sodium resin sulfonate.Each of the solutions was tested to determine its viscosity. Table IIidentifies each copolymer by giving the percent by weight of styrene andmaleic anhydride chemically combined therein and givesthe viscosity, incentipoises at 25 C., of the 0.5 percent aqueous solution of the sodiumresin sulfonate. In the table, styrene is abbreviated as S and maleicanhydride as MA.

Table II cps. at 25 0.

Run No.

Percent Percent It will be noted that a decrease below about 15 percentin the proportion of maleic anhydride in the coplymer compositionresulted in a large increase in the viscosity of the aqueous solutionsof the sulfonated resin products. This is believed to be due to anincrease in the extent of cross-linkage formation between the polymermole cules during the sulfonation as the composition of the copolymersis varied to approach that of polystyrene.

EXAMPLE 3 Another pair of experiments were carried out as in Example 2,except that the alkenyl aromatic resins employed were copolymers oferr-vinyltoluene and maleic anhydride. Table III identifies eachcopolymer by giving the percent by weight of vinyltoluene and maleicanhydride chemicaly combined therein. The table gives the viscosity, incentipoises at 25 C., of a 0.5 weight percent aqueous solution of thesodium resin sulfonate obtained in each experiment. Abbreviationsemployed in the table have the meanings given in the preceding examples.

Table III Copolymer Viscosity of Aqueous Run No. Solution of PercentPercent N a Resin VT MA I sulfonate,

cps. at 25 C.

EXAMPLE 4 Each of a seriesof copolymers of ar-vinyltoluene andacrylonitrile was sulfonated with sulfur trioxideat a temperature oflO-- C. using liquid sulfur dioxide as the reaction medium and each ofthe resulting granular resin sulfonic acids was dissolved in water andneutrali'z'e'd with sodium hydroxide to form an aqueous solutioncontaining 0.5 percent by weight of its sodium salt. The viscosity ofeach such aqueous solution was determined. The procedure in carrying outthese operations was similar to that described in Example 1. Prior tothe sulfonation, a portion of each of the copolymer starting materialswas tested to determine its solution viscosity, i. e. the viscosity incentipoises at 25 C. of a solution of 10 weight percent of the copolymerin toluene. The solution viscosity values are indicative of the relativeaverage molecular Weights of the copolymers, i. e. the solutionviscosities increase with increase in the molecular weight. It may bementioned that all of the unsulfonat'ed copolymer starting materialswere readily disp'ersible in liquid sulfur dioxide. Table IV identifieseach vinyltolueneacrylonitrile copolymer by giving the percent by weightof acrylonitrile chemically combined therein, gives the solutionviscosity of each copolymer starting material, and gives the viscosityin centipoises at 25 C. of an aqueous solution of the sodium salt of thesulfonated copolymer in 0.5 weight percent concentration. Vinyltolueneand acrylonitrile are abbreviated as VT and VCN, respectively.

From runs 3-5 of the table, it will be seen that an increase in themolecular weight, i. e. in the solution viscosity, of the copolymerstarting material results in an increase in the viscosity of the 0.5percent aqueous solutions of the sodium resin sulfonate products. Theviscosity values for the aqueous sodium resin sulfonate solutionsindicate that the copolymer of 75 percent vinyltolue'ne and 25 percentacrylonitrile employed in Example 8 became cross-linked during the'sulfonation to a greater extent than the polymers of loweracrylonitrile content which were employed in the other runs of thetable. All of the sulfonated products dissolved readily and completelyin water, presumably to form colloidal solutions thereof.

EXAMPLE 5 A separate portion of the copolymer of 95 weight percentvinyltoluene and 5 percent acrylonitrile having a solution viscosity of563, i. e. a copolymer of the kind and quality employed in run 4 ofTable IV, was sulfonated and the product tested. The procedure wassimilar to that employed in Example 4, except that the sulfonation wascarried out in a closed vessel under the autogenous pressure at roomtemperature, i. e. at about 25 C., instead of at l C. A 0.5 weightpercent solution of the sodium salt of the sulfonated copolymer in waterhad a viscosity of 1980 centipoises at 25 C. This result, when comparedwith that obtained in run 4 of Table 1", indicates that the extent ofcross-linkage formation during the sulfonation becomes greater as thesulfonation temperature is raised.

EXAMPLE 6 In each of a series of experiments, a copolymer of 95 weightpercent vinyltoluene and percent acrylonitrile, having a solutionviscosity of 563 centipoises at C.,

was s'ul'fonated with sulfur dioxide at a temperature of l0 C. usingliquid sulfur dioxide as the reaction medium. Each resin sultonic acidproduct was dissolved in water and neutralized with sodium hydroxide toform an aqueous solution containing 0.5 weight percent of the sodiumresin sulfonate. The proportion of liquid sulfur dioxide was varied fromone experiment to another so that the mixtures formed by the sulfonationreaction were slurries containing the precipitated resin sulfonic acidin different proportions. Table V gives the percent by weight ofgranular resin sulfonic acid in the slurry of the same and liquid sulfurdioxide obtained by each sulfonation reaction and gives the viscosity incentipoises at 25 C. of an aqueous solution consisting of 0.5

percent by weight of the sodium salt of the resin sulfonic aciddissolved in water.

Table 'V Wt. Percent of Resin Sull'onic 'Acid'ln Sulfonation Mixture Run'Nb.

IOnAb- Apparently, as the proportion of the liquid sulfur dioxidereaction medium 'is decreased, so that the proportion of the resinsulfonic acid increases from to 7 percent or higher, the formation ofcross-linkages between polymer molecules during the sulfonation occursto an increasing extent. 7

EXAMPLE 7 Ten grams of a copolymer of 96 weight percent vinyltoluene and4 percent acrylonitrile was dissolved in 200 ml. of liquid sulfurdioxide and the solution was cooled to 60" C. To the cold solution therewas added with stirring a solution of 5 ml. of liquid sulfur trioxide in50 ml. of liquid sulfur dioxide which latter solution has beenpre-cooled to '60 C. The resulting mixture was stirred for 45 minutes,during which time it warmed to -l0 C. and the copolymer sulfonic acidwas formed and precipitated. The product was separated, dissolved inwater, and neutralized with an aqueous sodium hydroxide solution to forman aqueous solution containing 0.5 percent by Weight of the sodium resinsulfonate. This aqueous solution had a viscosity of 400 centipoises at25 C. v

EXAMPLE 8 Ten grams of a copolymer of 90 weight percent vinyltoluene and10 percent acrylonitrile (which copolymer had a solution viscosity in 9times its weight of toluene of 5660 centipoises at 25 C.) was dissolvedin 400 ml. of liquid sulfur dioxide to form a solution having atemperature of 10 C. This copolymer solution was added, in from 5 to 10minutes and with stirring, to a solution of 5 ml. of liquid sulfurtrioxide and 850 ml. of liquid sulfur dioxide that was also at atemperature of 10 C. During the addition, the copolymer sulfonic acidwas formed and precipitated. The product was separated, dissolved inwater and neutralized with sodium hydroxide to form an aqueous solutioncontaining 0.5 weight percent of its sodium salt. This aqueous solutionhad a viscosity of 1170 centipoises at 25 C.

EXAMPLE 9 The alke'nyl aromatic resin employed in this experiment was acopolymer of weight percent of vinyltoluene and 25 percent ethylacrylate. Its solution viscosity, i. e. the viscosity of a 10 weightpercent solution of the same in toluene, was 10.5 centipoises at 25 C.Ten grams of the copolymer was dissolved in 400 ml.

of liquid sulfur dioxide at -10 C. This copolymer solution and asolution of 4.3 ml. of liquid sulfur trioxide in 400 ml. of liquidsulfur dioxide cooled to 10 C. were simultaneously fed to a vesselinitially containing 500 ml. of liquid sulfur dioxide, while stirringthe resulting mixture. The additions were made in about '12 minutes. Thecopolymer sulfonic acid thus formed and precipitated was separated,dissolved in water, and neutralized with sodium hydroxide to form anaqueous solution containing 0.5 weight percent of its salt. This aqueoussolution had a viscosity of centipoises at 25 C.

EXAMPLE The alhenyl aromatic resin employed in this experiment was acopolymer of 75 percent vinyltoluene and 25 percent methyl methacrylate.Its solution viscosity in 9 times its weight of toluene was 14.6centipoises at 25 C. A solution was prepared by dissolving 8.4 grams ofthe copolymer in 350 ml. of liquid sulfur dioxide cooled to --10 C.Another solution was prepared by dissolving 4.5 ml. of liquid sulfurtrioxide in 350 ml. of liquid sulfur dioxide at 10 C. The two solutionswere fed simultaneously and in about 10 minutes to a vessel whichinitially contained 405 ml. of liquid sulfur dioxide at a temperature of-10 C., while stirring the resulting mixture. The copolymer sulfonicacid was formed and precipitated during the addition. The product wasseparated, dissolved in water, and neutralized with sodium hydroxide toform an aqueous solution containing 0.5 percent by weight of its sodiumsalt. This aqueous solution had a viscosity of 5 centipoises at 25 C.

We claim:

1. A method for the production of water-soluble resin sulfonates whichcomprises admixing, with liquid sulfur dioxide, a solid thermoplasticpolymer containing in chemically combined form a total of at least 60percent by weight of at least one mono-alkenyl aromatic compound havingfrom 2 to 3 carbon atoms in its alkenyl group, which alkenyl groupcomprises a vinylidene radical and is attached directly to a carbon atomof the aromatic nucleus, and containing in the polymer moleculeradicals, selected from the class consisting of carbonyl, carbonyloxyand nitrile radicals, that are effective in solubilizing the polymerwith respect to liquid sulfur dioxide as a medium, Which polymercontaining the solubilizing radicals is capable of being dispersed bystirring in 19 times its weight of liquid sulfur dioxide to form a trueto colloidal solution that is'clear to cloudy in appearance and is freeof a distinct separate layer and is also free of a precipitate ofresinous material, forming such solution of the polymer in the liquidsulfur dioxide, and mixing with the solution at least 0.7 molecularequivalent of sulfur trioxide per molecular equivalent of alkenylaromatic compound chemically combined in the resin while maintaining themixture at a reaction temperature not higher than 40 C.

2. A method, as claimed in claim 1, wherein the liquid sulfurdioxide-dispersible polymeric starting material is one having at least60 percent by weight of a nuclear alkylated mono-alkenyl aromaticcompound of the benzene series chemically combined therein, from 0.8 to2 molecular equivalents of sulfur trioxide are employed per molecularequivalent of mono-alkenyl aromatic compound chemically combined in thepolymer, the polymer is dispersed in liquid sulfur dioxide, the sulfurtrioxide is dissolved in at least an equal weight of liquid sulfurdioxide, the two liquid bodies thus formed are admixed with one anotherto form a mixture which is at a reaction temperature between -40 and 30C. and which contains at least 9 parts by weight of liquid sulfurdioxide per part of the polymer starting material, and the mixture ismaintained at reaction temperatures between --40 and 30 C. until asulfonic acid of the polymer has been formed and precipitates from themixture.

3. A method, as claimed in claim 2, wherein the monoalkenyl aromaticcompound chemically combined in the polymer consists essentially ofar-vinyltoluene.

4. A method for the production of water soluble resin sulfonates whichcomprises admixing, with liquid sulfur dioxide, a solid thermoplasticpolymer containing in chemically combined form at least percent byweight of ar-vinyltoluene and also containing in the polymer moleculeradicals, selected from the class consisting of carbonyl, carbonyloxyand nitrile radicals, that are effective in solubilizing the polymerwith respect to liquid sulfur dioxide as a medium, which polymercontaining the solubilizing radicals is capable of being dispersed bystirring in 19 times its weight of liquid sulfur dioxide to form a trueto colloidal solution that is clear to cloudy in appearance and is freeof a distinct separate layer and is also free of a precipitate ofresinous material, forming such solution of the polymer by agitating themixture, forming a separate solution of sulfur trioxide in at least anequal weight of liquid sulfur dioxide, mixing the polymer solution andthe sulfur trioxide solution with one another in proportions such as tobring together from 0.8 to 2 molecular equivalents of sulfur trioxideand the polymer in amount containing 1 molecular equivalent of thechemically combined ar-vinyltoluene while maintaining the resultingmixture at reaction temperatures between -l0 and 30 0, whereby thepolymer is sulfonated and its sulfonic acid precipitates from themixture, separating the polymer sulfonic acid and neutralizing it withan alkali to obtain a water-soluble salt thereof.

5. A method, as claimed in claim 4, wherein the liquid sulfur dioxidesoluble polymeric starting material is a copolymer of from to 98 percentby weight of arvinyltoluene and from 2 to 35 percent of acrylonitrile.

6. A method, as claimed in claim 4, wherein the liquid sulfur dioxidesoluble polymeric starting material is a copolymer of from 60 to 87percent by weight of arvinyltoluene and from 13 to 40 percent of methylmethacrylate.

7. A method, as claimed in claim 4, wherein the liquid sulfur dioxidesoluble polymeric starting material is a copolymer of percent by weightof ar-vinyltoluene and 25 percent of ethyl acrylate.

8. A method, as claimed in claim 4, wherein the liquid sulfur dioxidesoluble polymeric starting material is a copolymer of from 68 to percentby weight of ar-vinyltoluene and from 5 to 32 percent maleic anhydride.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR THE PRODUCTION OF WATER-SOLUBLE RESIN SULFONATES WHICHCOMPRISES ADMIXING, WITH LIQUID SULFUR DIOXIDE, A SOLID THEREMOPLASTICPOLYMER CONTAINING IN CHEMICALLY COMBINED FORM A TOTAL OF AT LEAST 60PERCENT BY WEIGHT OF AT LEAST ONE MONO-ALKENYL AROMATIC COMPOUND HAVINGFROM 2 TO 3 CARBON ATOMS IN ITS ALKENYL GROUP, WHICH ALKENYL GROUPCOMPRISES A VINYLIDENE RADICAL AND IS ATTACHED DIRECTLY TO A CARBONATOMS OF THE AROMATIOC NUCLEUS, AND CONTAINING IN THE POLYMER MOLECULERADICALS, SELECTED FROM THE CLASS CONSISTING OF CARBONYL, CARBONYLOXYAND NITRILE RADICALS, THAT ARE EFFECTIVE IN SOLUBILIZING THE POLYMERWITH RESPECT TO LIQUID SULFUR DIOXIDE AS A MEDIUM, WHICH POLYMERCONTAINING THE SOLUBILIZING RADICALS IS CAPABLE OF BEING DISPERSED BYSTIRRING IN 19 TIMES ITS WEIGHT OF LIQUID SULFUR DIOXIDE TO FORM A TRUETO COLLOIDAL SOLUTION THAT IOS CLEAR TO CLOUDY IN APPEARANCE AND IOSFREE OF A DISTINCT SEPARATE LAYER AND IS ALSO FREE OF A PRECIPITATE OFRESINOUS MATERIAL, FORMING SUCH SOLUTION OF THE POLYMER IN THE LIQUIDSULFUR DIOXIDE, AND MIXING WITH THE SOLUTION AT LEAST 0.7 MOLECULAREQUIVALENT OF SULFUR TRIOXIDE PER MOLECULAR EQUILVALENT OF ALKENYLAROMATIC COMPOUND CHEMICALLY COMBINED IN THE RESIN WHILE MAINTAINING THEMIXTURE AT A REACTION TEMPERATURE NOT HIGHER THAN 40*C.